officers, border agents and state, local, and federal law enforcements. >> if you're speeding, you get pulled over, they're query that name. and if they're encountering a known or suspected terrorist it will pop up and say "call the terrorist screening center." >> reporter: how often do these encounters happen? >> we're averaging about 55 encounters with known or suspected terrorists every single day. >> reporter: in most cases, the encounters do not produce arrest but provide additional intelligence. >> location of where the guy is going, what he's doing, additional associates that the subject is hanging around. >> reporter: names are frequently added and subtracted, always in secret. healy also overseas the even more critical no-fly list. there are 20,000 people on the no-fly list. about 700 of them are americans. so there are people who live in this country who you have enough concerns about they can't fly? >> yes. >> reporter: the databases are not perfect. some innocent people have been kept off airplanes by mistake. and one person who never made the no fly list was umar farouk ab